Re: [PATCH v4 09/13] KVM: xen: automatically use the vcpu_info embedded in shared_info

[David Woodhouse]

On Tue, 2023-09-19 at 16:47 +0100, Paul Durrant wrote:
> 
> > 
> > I think they look interchangeable in this case. If we *do* take them
> > both in kvm_xen_set_evtchn_fast() then maybe we can simplify the slow
> > path where it set the bits in shared_info but then the vcpu_info gpc
> > was invalid. That currently uses a kvm->arch.xen.evtchn_pending_sel
> > shadow of the bits, and just kicks the vCPU to deliver them for
> > itself... but maybe that whole thing could be dropped, and
> > kvm_xen_set_evtchn_fast() can just return EWOULDBLOCK if it fails to
> > lock *both* shared_info and vcpu_info at the same time?
> > 
> 
> Yes, I think that sounds like a neater approach.
> 
> > I didn't do that before, because I didn't want to introduce lock
> > ordering rules. But I'm happier to do so now. And I think we can ditch
> > a lot of hairy asm in kvm_xen_inject_pending_events() ?
> > 
> 
> Messing with the asm sounds like something for a follow-up though.

AFAICT we can just delete the whole bloody lot. But yes, it's
definitely a later cleanup, enabled by the fact that we (will) now have
an agreed way of taking both locks at once, which I didn't want to do
in the first place.

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